Jan Oort

Jan Hendrik Oort (April 28, 1900 – November 5, 1992) was a prolific Dutch astronomer. He made many important contributions in the field of astronomy and was a pioneer in the field of radio astronomy. In 1932 he became the first person to discover evidence of dark matter. First proposed by Swiss astronomer Fritz Zwicky in the 1930s, at nearly the same time, Jan Oort in the Netherlands discovered that the density of matter near the Sun was nearly twice what could be explained by the presence of stars and gas alone. The Oort cloud of comets bears his name.

Some of Oort’s discoveries:

In 1924, Oort discovered the galactic halo, a group of stars orbiting the Milky Way but outside the main disk.

In 1927, he calculated that the center of the Milky Way was 5,900 parsecs (19,200 light years) from the Earth in the direction of the constellation Sagittarius.

In 1932, by measuring the motions of stars in the Milky Way he was the first to find evidence for dark matter, when he found the mass of the galactic plane must be more than the mass of the material that can be seen.

He showed that the Milky Way had a mass 100 billion times that of the Sun.

In 1950, he suggested that comets came from a common region of the Solar System (now called the Oort cloud).

He found that the light from the Crab Nebula was polarized, and produced by synchrotron emission.